1. Field of the Invention
The present invention relates to a High Voltage Direct Current (abbreviated as “HVDC” hereinafter) system and more particularly, to a method for correcting electric power loss generated between an electric power transmission station and an electric power receiving station of an HVDC system.
2. Background of the Invention
The HVDC system means an electric power transmission system that an electric power transmission station converts an alternating current electric power generated by an electric power station to a direct current electric power to transmit the electric power and then an electric power receiving station reconverts the direct current electric power to the alternating current electric power to supply the electric power.
The HVDC system is applied to undersea cable electric power transmission, large capacitor long-distance electric power transmission, interconnection among alternating current grids, etc. Also, the HVDC system enables interconnection in grids having different frequencies and asynchronism interconnection.
The electric power transmission station converts an alternating current electric power to a direct current electric power. That is, since the status that the alternating current electric power is transmitted using an undersea cable, etc. is very dangerous, the electric power transmission station converts the alternating current electric power to the direct current electric power and then transmits the electric power to the electric power receiving station.
Meanwhile, various kinds of voltage converters are used for the HVDC system, and a modular multi-level type voltage converter has recently received much attention.
The modular multi-level converter (can be abbreviated as “MMC”) is a device that converts an alternating current electric power to a direct current electric power by using a plurality of sub-modules, and is operated by controlling each sub-module in any one of states of charge, discharge and bypass.
A central controller calculates the amount of transmission electric power transmitted from the electric power transmission station by using a voltage value and a current value, which are acquired through a metering transformer installed in the electric power transmission station.
Also, the central controller calculates the amount of electric power received by the electric power receiving station by using a voltage value and a current value, which are acquired through a metering transformer installed in the electric power receiving station.
Also, the central controller calculates the amount of electric power loss on the basis of a difference between the amount of transmission electric power and the amount of received electric power. However, in the related art, the difference value between the amount of transmission electric power and the amount of received electric power is simply recognized as the amount of electric power loss.
The HVDC system is designed and studied considering switching loss of each device, heat loss caused by impedance components, and harmonic wave loss.
However, a theoretical design value always has an error, and a range of the error is represented as a considerably high loss during actual system operation. Therefore, the HVDC system cannot be operated accurately due to the loss caused by the error, and the loss is recognized as a loss which is not generated actually. That is, it is difficult to measure the exact amount of electric power loss by simply using the difference value between the amount of transmission electric power and the amount of received electric power.
In this respect, a method for measuring actual loss by installing a plurality of current sensors, a plurality of voltage sensors, and a monitoring device in each device or electric line may be provided. However, it is difficult to actually apply this method to the system due to installation of too many devices, and even though the method is applied to the system, a problem occurs in that the cost is increased.